Experimental methodology for obtaining fatigue crack growth rate curves in mixed-mode I-II by means of variable cyclic displacement tests

This work presents a novel procedure to characterize the crack growth rate curve under fatigue mixed mode I + II loading conditions with only one specimen. The procedure is based on applying a variable cyclic displacement during a Mixed Mode Bending (MMB) test together with a real time monitoring of the specimen's compliance. The method introduces a dynamic compliance calibration for the crack length monitoring that relates the dynamic compliance to the visually obtained crack length using digital recording of the crack tip region during the fatigue test. The testing procedure is validated to be efficient in terms of testing time and required material.